Installation comprising steam turbine modules with optimized efficiency

ABSTRACT

An installation includes a high pressure steam turbine module, a medium pressure steam turbine module, and at least one low pressure steam turbine module, sealing devices being positioned between a rotating turbine shaft and corresponding casings of the various turbine modules, each of the modules include a main chamber in which the turbine is housed. The installation also includes a first collection chamber positioned in the casing of the high pressure module to collect the steam leaks leaving the high pressure module through its sealing device at a pressure greater than atmospheric pressure, and an injection chamber positioned in the casing of the low pressure module and connected by a first circuit to the first collection chamber such that the steam is transferred from the first collection chamber toward the injection chamber, and then toward the main chamber of the low pressure module through its sealing device.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application hereby claims priority under 35 U.S.C. Section 119 to French Patent application number 1158830, filed Sep. 30, 2011, the entire contents of which are hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates to the field of nuclear installations comprising steam turbine modules. This type of installation is generally composed of a plurality of turbine modules, including a high pressure module, one or more low pressure modules, and an intermediate medium pressure module. Each module can be configured in a single flow or double flow arrangement. The installation is intended to generate electricity by means of an alternator driven by the turbine modules. The installation may operate on fossil fuel or nuclear power.

BACKGROUND

An installation of the known type has a rotating turbine shaft connecting the rotors of the various modules. Each rotor is housed in a casing. Sealing devices are positioned between the turbine shaft and each of the casings. A leak of steam occurs at the sealing devices. In the prior art, the leakage occurring at the sealing device of the high pressure module is collected and sent to a leak collection system.

Devices of this type have, notably, the disadvantage of having a considerable ingress of air into the steam cycle through the low pressure modules, because the latter are at a lower pressure than the atmosphere. This ingress of air leads to a change in the thermodynamic characteristics of the steam, thus reducing efficiency. Moreover, since the steam working in the low pressure modules is close to saturation, this ingress of air may also lead to the appearance of water droplets which may damage a condenser located at the outlet of the low pressure module. According to the prior art, one solution to this problem is to create a live steam feed in the low pressure modules, said live steam being taken off at the source, i.e. in the steam generator. This does indeed limit the ingress of air, but has the drawback of limiting the work of the live steam in the steam flow.

The invention is intended to overcome some or all of these drawbacks and improve the efficiency of the installation by optimizing the steam cycle.

SUMMARY

The present disclosure is directed to an installation including a high pressure steam turbine module, a medium pressure steam turbine module, and at least one low pressure steam turbine module, sealing devices being positioned between a rotating turbine shaft and corresponding casings of the various turbine modules, each of the modules comprising a main chamber in which a turbine is housed. The installation further includes a first collection chamber positioned in the casing of the high pressure module to collect steam leaks leaving the high pressure module through its sealing device at a pressure greater than atmospheric pressure, and an injection chamber positioned in the casing of the low pressure module and connected by a first circuit to the first collection chamber in such a way that the steam is transferred from the first collection chamber toward the injection chamber, and then toward the main chamber of the low pressure module through its sealing device.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will become clear in the light of the following description, with reference to the attached drawings, in which, by way of exemplary illustration,

FIG. 1 shows an installation according to the invention,

FIG. 2 shows a variant of the installation of FIG. 1,

FIG. 3 is an axial cross section through the sealing device of the high pressure module of FIG. 2,

FIG. 4 is an axial cross section through the sealing device of the medium pressure module of FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Introduction to the Embodiments

In a first aspect, the installation comprises a high pressure steam turbine module, a medium pressure steam turbine module, and at least one low pressure steam turbine module, sealing devices being positioned between a rotating turbine shaft and the corresponding casings of the various steam turbine modules, each of the modules comprising a main chamber in which the turbine is housed,

the installation further comprising:

-   -   a first collection chamber positioned in the high pressure         module casing so as to collect the steam leaks leaving said high         pressure module through its sealing device at a pressure greater         than atmospheric pressure, and     -   an injection chamber positioned in the low pressure module         casing and connected by a first circuit to the first collection         chamber in such a way that the steam is transferred from the         first collection chamber toward the injection chamber, and then         toward the main chamber of the low pressure module through its         sealing device, at a pressure greater than atmospheric pressure.         These characteristics make it possible to minimize or even         eliminate any live steam feed to the low pressure module sealing         device, thereby notably improving the efficiency of the         installation. According to another characteristic, the         installation comprises a second collection chamber positioned in         the medium pressure module casing in such a way that the steam         leaks leaving the medium pressure module through its sealing         device are collected, and said leaks are transferred via the         first circuit toward the injection chamber. This enables the         steam feed to be supplemented in order to feed the low pressure         module sealing device and further improve the efficiency of the         installation by reducing the live steam requirement.

According to a specific characteristic, the installation comprises a third collection chamber positioned between the main chamber of the high pressure module and the first collection chamber casing in such a way that the leaks of steam from the high pressure module through its sealing device are collected and said leaks are directed via a conduit toward the main chamber of the medium pressure module or toward an inlet of the main chamber of the low pressure module. This enables the steam cycle to be further optimized by using the energy of the steam obtained from the high pressure module leaks in the working cycle of the medium pressure module or the low pressure module.

According to a specific characteristic, the third collection chamber is kept at a pressure level between the pressure inside the high pressure module casing and the pressure in the first collection chamber. This arrangement enables the recovery of steam leaks to be optimized at the sealing device of the high pressure module.

According to a specific characteristic, each sealing device of the various steam turbine modules has a fourth collection chamber positioned in the casing of the module concerned, said fourth collection chamber having a pressure lower than atmospheric pressure, so as to collect not only the leaks of steam leaving said module through its sealing device but also any air entering from outside the casing concerned. Because of this characteristic, the ingress of air into the various modules and the leakage of steam toward the outside are both effectively prevented. In this context, the term “inside” applied to a module signifies the space within the casing, and the term “outside” signifies the external space extending beyond the limit defined by the casing of said module.

According to a specific characteristic, each fourth collection chamber is connected by a conduit to a second circuit at a lower pressure than atmospheric pressure. Because of this characteristic, the air and steam collected in the fourth chambers can be effectively sucked out and removed.

According to a specific characteristic, the first circuit has a pressure control device which keep its pressure at a level above atmospheric pressure. Because of this characteristic, steam can be transferred from the first and/or second chambers toward the injection chamber.

DETAILED DESCRIPTION

FIG. 1 shows an installation according to the invention, with its steam circuits. The installation comprises a high pressure steam turbine module 1, a medium pressure steam turbine module 2, and one or more low pressure steam turbine modules 3. The high pressure turbine is fed with live steam, in other words with steam from a steam generator 4, such as a nuclear powered steam generator. The steam leaving the high pressure module 1 is guided by a conduit 41 through a drier/superheater 42 toward the inlet of the medium pressure module 2. The steam leaving the medium pressure module 2 is guided by a conduit 43 toward the inlet of the low pressure module 3. The outlet of the low pressure module 3 is connected to a steam condenser 6.

The rotors of the various modules 1, 2, 3 are interconnected to form a rotating turbine shaft 5. Each rotor is housed in a casing 10, 20, 30 belonging to the modules 1, 2, 3 respectively, and more precisely in respective main chambers 1′, 2′, 3′ of said modules 1, 2, 3 in which the turbine operates. Sealing devices 100, 200, 300 a, 300 b are positioned between the turbine shaft 5 and the casings 10, 20, 30 of the various modules.

The sealing device 100 of the high pressure module 1 comprises three sealing gaskets, namely a first gasket 11 on the end nearest the module 1, a third gasket 13 on the end outside the module 1, and a second gasket 12 between the first 11 and third 13 gaskets. The first gasket 11 causes a leak F11 of steam from the main chamber 1′ of the high pressure module 1 toward a first collection chamber C1 positioned in the casing 10 of the high pressure module 1. The first collection chamber C1 is connected by a conduit 15 to a first circuit 61.

A fourth collection chamber C4 is positioned in the casing 10 of the high pressure module 1 between the second and third gaskets 12, 13, and collects both the leaks F12 from the second gasket 12 and the ambient air sucked in at F13 through the third gasket 13. For this purpose, the fourth collection chamber is kept at a pressure slightly below atmospheric pressure, by connecting this chamber C4 by a conduit 14 to a second circuit 60, also known as the condensate circuit: the pressure is kept at a level PC, close to 0.95 bar (C4). The pressure reduction is obtained by means of the condenser 6 to which the second circuit 60 is connected. The other three sealing devices are each fitted with a pressure reduction system of this type using a fourth collection chamber C24, C4 a, C4 b.

It should be noted that the values stated herein are for guidance only and may be subject to a percentage error close to unity, in other words an error of approximately 1%.

In this case, the low pressure module 3 is a double flow module. It is provided with a sealing device 300 a, 300 b at each end, in a symmetrical arrangement. Each sealing device 300 a, 300 b comprises three gaskets, namely a first gasket 31 a, 31 b in the module 3, a third gasket 33 a, 33 b in the module 3, and a second gasket 32 a, 32 b between the first and third gaskets. The first gasket 31 a, 31 b allows an injection of steam F31 toward the main chamber 3′ of the casing 30 from an injection chamber Ca, Cb positioned in the casing 30 of the low pressure module 3.

A fourth collection chamber C4 a, C4 b is positioned in the casing 30 of the high pressure module 3 between the second and third gaskets 32 a, 33 a, 32 b, 33 b, and collects both the leaks F32 a, F32 b from the second gasket 32 a, 32 b and the ambient air sucked in at F13 a, F13 b through the third gasket 33 a, 33 b. The pressure in the fourth chamber C4 a, C4 b is reduced by means of conduits 34 a, 34 b connecting this chamber to the second circuit 60 in the same way as for the fourth chamber C4 of the high pressure module 1.

The injection chamber Ca, Cb is connected via a conduit 35 a, 35 b to the first circuit 61 and to the first collection chamber C1 (via the conduit 15) in such a way that the steam is transferred from the first collection chamber C1 toward the injection chamber Ca, Cb, and then toward the main chamber 3′ of the low pressure module 3 through its sealing device 300 a, 300 b. More precisely, the steam introduced into the injection chamber Ca, Cb is at a higher pressure than the pressure present in the main chamber 3′ of the low pressure module 3, and the leak F31 a, F31 b at the gasket 31 a, 3 ab allows this steam to enter the casing 30. For this purpose, the first circuit 61 is kept at a pressure PR close to 1.15 bar, slightly above atmospheric pressure, while the inside of the casing 30 is connected to the condenser 6 and is therefore kept at a pressure slightly below atmospheric pressure. In order to provide the pressure in the first circuit 61 it is possible to take live steam from the steam generator 4 by means of a reducer 44 and a conduit 45. The first circuit 61 is also called the controlled circuit.

The steam from the leaks F11 at the sealing device 100 of the high pressure module 1 is recovered and introduced into the low pressure module 3 by feeding into the sealing device 300 a, 300 b at the position of the leak F31 a, F31 b. This makes it possible to minimize or even eliminate any live steam feed through the reducer 44, thereby notably improving the efficiency of the installation. The live steam is then exclusively reserved for introduction into the high pressure module 1 where it produces the maximum work for electrical power generation.

The sealing device 200 of the medium pressure module 2 comprises three gaskets, namely a first gasket 21, a third gasket 23, and a second gasket 22 between the first 21 and third 23 gaskets. The first gasket 21 causes a leak F21 of steam from the main chamber 2′ of the high pressure module 2 toward a second collection chamber C2 positioned in the casing 20 of the high pressure module 2. The first collection chamber C2 is connected by a conduit 25 to a first circuit 61. It is kept at a pressure PR close to 1.15 bar, slightly above atmospheric pressure. Thus the steam leaks F21 from the medium pressure module 2, in particular from its main chamber 2′, through the gasket 21 are transferred via the conduit 25, the first circuit 61 and the conduit 35 a, 35 b into the injection chamber Ca, Cb and then toward the main chamber 3′ of the low pressure module 3 through the gasket 31 a, 31 b. The steam from the leaks F21 at the sealing device 200 of the medium pressure module 2 is thus recovered and is then introduced into the low pressure module 3 by feeding into the sealing device 300 a, 300 b and, in particular, into the main chamber 3′ in which the turbine operates. This makes it possible to supplement the feed provided by the leaks F11 from the high pressure module 1, and thus to minimize further, or even eliminate, any live steam feed through the reducer 44 and further improve the efficiency of the installation.

A fourth collection chamber C24 is positioned in the casing 20 of the medium pressure module 2 between the second and third gaskets, and collects both the leaks F22 from the second gasket 22 and the ambient air sucked in at F23 through the third gasket 23. The pressure in the fourth chamber C24 is reduced by means of a conduit 24 connecting this chamber to the second circuit 60 in the same way as for the fourth chamber C4 of the high pressure module.

FIG. 2 shows the installation of FIG. 1 with the addition of the variant described below. The sealing device 101 of the high pressure module 1 comprises a fourth sealing gasket 16 positioned between the main chamber 1′ of the high pressure module 1 and the first gasket 11. The fourth gasket 16 causes a leak F16 of steam from the main chamber 1′ of the high pressure module 1 toward a third collection chamber C3 positioned in the casing 10 of the high pressure module 1. The third collection chamber C3 is connected by a conduit 55 to a working steam inlet 56 of the medium pressure module 2 or to the conduit 43 feeding the low pressure module 3. Thus the third collection chamber C3 is positioned between the inside of the casing 10 of the high pressure module 1 and the first collection chamber C1 in such a way that the leaks of steam F16 leaving said high pressure module 1, and in particular its main chamber 1′, through its sealing device 101 are collected, and these leaks are directed, via the conduit 55, toward the main chamber 2′ of the medium pressure module 2 or toward an inlet of the main chamber 3′ of the low pressure module 3. This enables the steam cycle to be further optimized by using the energy of the steam obtained from the high pressure module leaks in the working cycle of the medium pressure module or the low pressure module.

The pressure in the third collection chamber is kept at a level PT between the pressure inside the high pressure module casing 10 (close to 11.5 bar) and the pressure in the first collection chamber C1 (close to 1.15 bar). In the example, the pressure of the third collection chamber C3 is close to 3 bar.

FIG. 3 shows the sealing device 101 of the high pressure module 1 of FIG. 2. The casing 10, also called the outer body of the module, can be seen here. This casing receives the end of the rotor 50 connected to the rotating shaft 5. The three chambers C1, C3, C4 are positioned in the end of the casing 10. The third collection chamber C3 is positioned between the main chamber 1′ of the casing 10 of the high pressure module 1 and the first collection chamber C1.

A channel 19 formed in the casing 10 directs the leaks F16 of steam from the main chamber 1′ of the high pressure module 16 through the fourth gasket 16 toward the third collection chamber C3. These leaks are then directed via the conduit 55 toward a working stage (inlet 56) of the low pressure module 2 or toward the inlet of the main chamber 3′ (conduit 43) of the low pressure module 3.

A channel 17 formed in the casing directs the leaks F11 of steam through the first gasket 11 toward the first chamber C1. The steam collected in the chamber C1 is then transferred toward the injection chamber Ca, Cb of the low pressure module 3 via the conduit 15 and the first circuit 61.

A channel 18 formed in the casing directs the leaks F12 of steam through the second gasket 12, together with the air entering through the third gasket 13, toward the first chamber C4 at reduced pressure. The air and steam reaching the fourth chamber C4 are sucked into the second circuit 60 through the conduit 14. This arrangement enables the ingress of air into the high pressure module to be prevented.

It should be noted that the first and second gaskets 11, 12 are composed of two annular gasket elements, that the fourth gasket 16 is composed of four annular gasket elements, and that the third gasket 13 is composed of a single annular element.

In order to apply the sealing device of FIG. 3 to the installation of FIG. 1, it is simply necessary to remove the third chamber C3, the channel 19 and the gasket 16.

FIG. 4 shows the sealing device 200 of the medium pressure module 2 of FIGS. 1 and 2. The casing 20, which receives the end of the rotor 50 connected to the rotating shaft 5, can be seen. The two chambers C2, C24 are positioned in the end of the casing 20. The second collection chamber C2 is positioned between the main chamber 2′ of the medium pressure module 2 and the fourth collection chamber C24.

A channel 27 formed in the casing 20 directs the leaks F21 of steam from the main chamber 2′ of the medium pressure module 2 through the first gasket 21 toward the second collection chamber C2. These leaks are then transferred toward the injection chamber Ca, Cb of the low pressure module 3 via the conduit 25 and the first circuit 61.

A channel 28 formed in the casing directs the leaks F22 of steam through the second gasket 22, together with the air entering through the third gasket 23, toward the first chamber C24 at reduced pressure. The air and steam reaching the fourth chamber C4 are sucked into the second circuit 60 through the conduit 24.

The first and second gaskets 21, 22 are composed of two annular gasket elements. The third gasket 23 is composed of a single annular element.

The arrangement of the sealing device 300 a, 300 b of the low pressure module 3 is the same as that shown in FIG. 4 for the medium pressure module 2.

Each of the first, second, third and fourth chambers C1, C2, C3, C4, C24, C4 a, C4 b, as well as the injection chambers Ca, Cb, communicate directly through at least one channel 17, 27, 19, 18, 28 positioned in the casings 10, 20, 30 with a leak passage between said turbine shaft 5 and the respective casings 10, 20, 30. Each of the channels opens into said leak passage between two annular sealing gaskets 11, 12, 13, 16, 21, 22, 23, 31 a, 32 a, 33 a, 31 b, 32 b, 33 b.

In practice, the steam flow rates of the various leaks between the rotating shaft and the gaskets are adjusted by regulating the permeability of the passage between the gasket and the shaft. This permeability is adjusted by specifying the amount of clearance between the shaft and the gaskets. It can also be adjusted by varying the number of annular gasket elements used.

The installation of FIG. 1 is particularly suitable for a configuration comprising three low pressure modules 3. As for the installation of FIG. 2, this is particularly suitable for a configuration comprising two low pressure modules 2.

Alternatively, in a preferred embodiment, the installation may have a single casing enclosing both the high pressure steam turbine module and the medium pressure steam turbine module (not shown in the drawings). In this case, the first collection chamber (C1) and the second collection chamber (C2) are placed in the same casing, each of said first and second collection chambers being located at the outlets of the high and medium pressure turbine modules respectively, through their sealing device, at a pressure greater than atmospheric pressure.

This installation, notably of a nuclear type, is preferably designed to receive a large flow of saturated steam at low temperature and low pressure. In particular, the high and medium pressure turbine module is designed to receive a flow of saturated steam of more than 5000 tonnes per hour, preferably more than 8000 tonnes per hour, at low temperature, in other words below 350° C., preferably below 300° C., and at pressures of less than 100 bar.

Finally, the escape or the discharge pressure at the interface between the high and medium pressure turbine module and the low pressure turbine module is preferably less than 10 bar.

It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover all modifications which are within the spirit and scope of the invention as defined by the appended claims; the above description; and/or shown in the attached drawings. 

What is claimed is:
 1. An installation comprising a high pressure steam turbine module, a medium pressure steam turbine module, and at least one low pressure steam turbine module, sealing devices being positioned between a rotating turbine shaft and corresponding casings of the various turbine modules, each of the modules comprising a main chamber in which a turbine is housed, the installation further comprising: a first collection chamber positioned in the casing of the high pressure module to collect steam leaks leaving said high pressure module through its sealing device at a pressure greater than atmospheric pressure, and an injection chamber positioned in the casing of the low pressure module and connected by a first circuit to the first collection chamber such that the steam is transferred from the first collection chamber toward the injection chamber, and then toward the main chamber of the low pressure module through its sealing device.
 2. The installation as claimed in claim 1, wherein a second collection chamber is positioned in the casing of the medium pressure module so as to collect steam leaks leaving said medium pressure module through its sealing device at a pressure greater than atmospheric pressure, and transfer said leaks, via said first circuit, toward said injection chamber.
 3. The installation as claimed in claim 1, wherein a third collection chamber is positioned between the main chamber of the high pressure module and said first collection chamber in such a way that the steam leaks leaving said high pressure module through its sealing device at a pressure greater than atmospheric pressure are collected and said leaks are directed, via a conduit, toward the main chamber of the medium pressure module or toward an inlet of the main chamber of the low pressure module.
 4. The installation as claimed in claim 3, wherein the pressure in the third collection chamber is kept at a pressure level between a pressure in the main chamber of the high pressure module and a pressure in the first collection chamber.
 5. The installation as claimed claim 1, wherein each sealing device of the various steam turbine modules has a fourth collection chamber positioned in the casing of the module concerned, said fourth collection chamber having a pressure lower than atmospheric pressure, so as to collect not only the leaks of steam leaving said module through its sealing device but also air entering from outside the casing concerned.
 6. The installation as claimed in claim 5, wherein each fourth collection chamber is connected by a conduit to a second circuit at a pressure lower than atmospheric pressure.
 7. The installation as claimed in claim 1, wherein said first circuit has a pressure control device which keeps its pressure at a level above atmospheric pressure.
 8. The installation as claimed in claim 1, wherein each of said chambers communicates directly through at least one channel with a leak passage between said turbine shaft and the respective casings.
 9. The installation as claimed in claim 8, wherein each of said channels opens into said leak passage between two annular sealing gaskets. 